352 CRESSWKLL SHKARER. 



necessary to suppose tliat tlie Kotifers sepanited from the 

 main stem of tlie Annelida at a stage earlier tlian tliat of the 

 formation of a definite mesoderm, wliile Dinophilus arose 

 only after the coelo-mesoblast had definitely appeared. On 

 the whole, Dinophilns is not so closely allied to the 

 Rotifers as Histriobdelhi. Unfortunately our lack of 

 information with regard to the development of the coelo-meso- 

 blast in Histriobdella prevents our forming any opinion as 

 to how mncli it resembles the Kotifers in this i-espect. 



It is remarkal)le with regard to the llotifers that, despite 

 their wide distribution and their great number of species, so 

 comparatively few marine forms should be known. What 

 has become of these if they have ever existed ? Are forms 

 like Belatro and Hemidasys (Claparede, 4), Turbanella 

 (Schultz, 29), or the Echinoderes (Zelinka, 37) to be looked 

 npon as the modified descendants of a marine branch of 

 these animals ? Here Ave have a marked metamerism coupled 

 with the main features that characterise both Histriobdella 

 and the Kotifers. It is possible that it is with some of 

 these somewhat obscure groups that the relationship of 

 Histriobdella really lies. 



In conclusion, it may be stated that our present knowledge 

 does not warrant us farther than to conclude that Histrio- 

 bdella is a highly specialised form, retaining many Kotiferan 

 features, and that it is to be grouped with Dinophilus as a 

 primitive Annulate, but not directly related to Polygordius 

 and Protodrilus. 



Summary. 



(1) Histriobdella liomari is a normal inhabitant of the 

 branchial chamber of the European lobster. It is found in 

 equal numbers throughout the year, on both the male and 

 female. 



(2) The anterior feet of the head, unlike those of Stratio- 

 drilus, are non-retractile. 



(3) There are four pairs of nephridia in both sexes. They 

 are closed, and are of the primitive flame-cell type similar to 



